The cylinders of heavy-duty internal combustion engines, such as truck engines, are often overhauled for maintenance and repair purposes. Heavy-duty gas and diesel engines usually include cylinder sleeves which are removable from the engine block, and in the regular maintenance of such engines the cylinder sleeves may be removed and the worn sleeves replaced along with replacement of the O-rings used to seal the cylinder sleeves with respect to the engine block.
When overhauling an engine it is usually required, in addition to removing and replacing the cylinder sleeves, to recondition the surface of the engine chamber walls adjacent the cylinder sleeve seal, and this reconditioning usually includes the boring out of the chamber walls concentric to the cylinder sleeve chamber. Such a boring operation may be accomplished by conventional machine tools, such as a milling machine, if the engine is removed from the vehicle. However, considerable time and expense may be eliminated if this boring operation can be accomplished while the engine remains within the vehicle, and in my U.S. Pat. No. 3,331,266 I disclose a boring tool for accomplishing this purpose.
In the boring tool shown in U.S. Pat. No. 3,331,266 a housing is mounted upon an engine block having a portion concentric to an engine cylinder sleeve chamber, and a rotatable driveshaft is supported upon the housing having a cutting tool attached thereto whereby rotation and axial displacement of the tool will accomplish the desired chamber wall reconditioning. Rotation of the driveshaft is by an electric drill associated with a chain and sprocket drive connection for rotating the driveshaft, and axial movement of the driveshaft and tool during the cutting operation is accomplished by hydraulic pump structure.
The pump structure includes a piston fixed upon the driveshaft and the driveshaft-piston moves within a cylinder within the housing. The cylinder is filled with hydraulic oil, and a circumferential spiral groove defined in the piston periphery functions as a pump to transfer fluid from one side of the piston to the other during driveshaft rotation. This pumping or transfer of the fluid imparts a linear movement to the driveshaft prducing the tool feed.
For rapid traverse of the driveshaft and tool, a fluid passage bypass system exists within the driveshaft controlled by a manually operated valve wherein fluid is readily transferred across the piston upon the opening of the valve. The valve is manually actuated by a control handle extending axially through the driveshaft structure.
In my U.S. Pat. No. 3,331,266 considerable machining of the driveshaft is required to produce the bypass passages and the valve structure requires extensive machining and a plurality of components requiring assembly, including a compression spring. In the event of spring breakage the tool may advance too rapidly with attendant damage to the tool or the engine block.
It is an object of the invention to provide a boring tool of the aforedescribed type wherein the fluid bypass about the driveshaft piston is simplified without adversely affecting the operating characteristics of the tool and economies in manufacture and assembly are experienced.
Another object of the invention is to provide a boring tool of the aforedescribed type wherein valve structure is incorporated in the driveshaft piston, and the valve structure is operated by rotation of the driveshaft, and does not require complex manual actuation apparatus.
In the practice of the invention a boring tool of the aforedescribed type utilizes piston structure comprising a two-part assembly wherein a portion of the piston is fixed to the tool supporting driveshaft, and another portion of the piston is capable of limited rotational movement to the first piston portion. Fluid passages within the two piston portions constitute valve structure wherein alignment of the passages at one rotational orientation of the piston portions permits fluid flow through the piston, while misalignment of the piston portion passages prevents such bypass flow during rotation of the driveshaft in a tool cutting direction.
The degree of relative rotation between the piston portions is limited by rotation limiting means consisting of a pin within a slot. Engagement of the pin with one end of the slot aligns the piston passage portions to open the bypass passages, while engagement of the pin with the other end of the slot constitutes the passage closed condition. An external accessible handle permits manual rotation of the driveshaft to position the piston portion passages to control the rapid traverse bypass operation .